1. Field
The present invention relates to a power supply circuit.
2. Description of the Related Art
Along with a demand for low power consumption recent years, with respect to electronic apparatuses, a semiconductor integrated circuit which includes a CPU, a RAM and the like which are operated at a low voltage (for example, 2V or less) has been developed and used. On the other hand, it is often the case that an operational voltage cannot be lowered in peripheral circuits such as various interfaces or input/output circuits (I/O). Accordingly, in such a case, a multi-output power supply circuit which can output a plurality of different voltages becomes necessary.
As shown in FIG. 9, a conventional multi-output power supply circuit 100 includes a first DC-DC converter 101 and a second DC-DC converter 102.
A power-supply voltage VIN is inputted to the first DC-DC converter 101 from a battery or an AC adapter. The first DC-DC converter 101 converts the power-supply voltage VIN into a predetermined first voltage V1, and outputs the first voltage V1 therefrom. Further, the second DC-DC converter 102 generates a second voltage V2 by boosting or lowering an output voltage Vo1 of the first DC-DC converter 101, and outputs the second voltage V2 therefrom.
The second DC-DC converter 102 is configured to receive the output voltage Vo1 as an input. Accordingly, it is necessary to operate the second DC-DC converter 102 after the output voltage Vo1 of the first DC-DC converter 101 sufficiently rises.
Accordingly, the above-mentioned conventional multi-output power supply circuit 100 includes a power-on control circuit 103. The power-on control circuit 103 detects that the output voltage Vo1 of the first DC-DC converter 101 becomes a threshold voltage Vth or more, and operates the second DC-DC converter 102 at this detection timing. The threshold voltage Vth is, for example, a voltage which is 90% of the first voltage V1.